Some of the wettest months on record have ensured an oversupply of nutrients in Lake Champlain and elsewhere, heightening the risk of blue-green algae blooms that sometimes contain toxins. Experts say the high waters of late could also translate into increased levels of E. coli, which can signal the presence of other unhealthy bacteria.

“The concern with all the extra rain would be all the extra runoff that’s going into the lakes, so we see more potential for blooms because of excess nutrients in the water,” said Sarah Vose, state toxicologist at the Vermont Department of Health. “And as a general rule, when it’s raining, you can expect E. coli levels are going to be higher.”

More than 200 trained volunteer monitors have begun surveying spots across Lake Champlain, where the thick blooms are most prevalent. Vose said the state has monitors taking samples from other bodies of water across Vermont in the event that blooms crop up there as well.

“Lakes that are more shallow that have swimming areas that tend to get a lot of use, those can frequently get blooms over the summer,” Vose said.

The micro-organisms that can lead to gastrointestinal problems for people are less easily detected. Neil Kammen, head of the Monitoring, Assessment and Planning Program at the Vermont Department of Environmental Conservation, said numerous state and local agencies collaborate to keep up an extensive water quality testing regimen in popular bodies of water.

The Department of Forests, Parks and Recreation, for instance, monitors swimming areas in its jurisdiction “on a pretty tight weekly schedule,” according to Kammen, and municipalities often do their own testing.

Kammen said years of testing data show that rivers tend to carry higher levels of bacteria than lakes or ponds. And his department teams up with river steward organizations across the state to monitor E. coli levels in popular swimming holes.

“And so in the same way that state parks will monitor and post signage on a beach, volunteer groups monitor swim holes.”

Kammen and Vose said the best way to avoid bacteria during a summer when water has a higher likelihood of containing lots of them is to confine water play to managed beaches and swimming holes, where warning signs are likely to be posted should levels merit concern.

Sticking to well-maintained, supervised beaches on ponds and lakes especially, Kammen said, will protect Vermonters from the most dangerous product of the heavy rains: swift currents and the debris they carry.

“When the water is perpetually high like this in a period when everybody is out recreating and it’s hot, that is a recipe for disaster, as we’ve seen,” Kammen said, noting two drowning deaths in recent weeks. “Now would be the perfect time to think about swimming at a state park as opposed to swimming in the Huntington Gorge.”